As devices that drive rotary machines, such as a compressor, there are devices including an electric device that generates a rotational drive force, and a transmission device that shifts the rotational drive force generated by the electric device to transmit the changed speed to rotary machines.
Patent Document 1 discloses a device using a constant speed electric motor and a variable speed electric motor for speed change as electric devices and using a planetary gear transmission device as a transmission device, in order to accurately control a speed change ratio. In this device, the rotational speed of an output shaft of a transmission device connected to a rotary machine can be changed by changing the rotational speed of the variable speed electric motor.